Device for scanning a thread by an optical beam

ABSTRACT

The invention relates to a device for scanning a thread, which is displaceable in the longitudinal direction thereof inside a measuring slot, by means of an optical beam emitted by a light source. The device includes a receiver of light reflected on the thread and a unit for processing electrical signals received by the receiver. The aim of the invention is to develop a small-sized device which is easy to operate and which makes it possible to detect foreign matter contained in the thread in a most selective manner at a high sensitivity. For this purpose, the light emission in at least two wavelength ranges is carried out by means of a light source, with these wavelength ranges being determined by two main wavelengths.

The invention relates to a device for scanning a yarn that is moved inits longitudinal direction in a measuring gap with a light beam from alight source, which device has a receiver for light reflected by theyarn and a unit for processing electrical signals from the receiver.

Such a device is known, for example, from EP 0 761 585, in which thereis provided a light source which emits light which on the one hand isreflected and on the other hand is also shaded by the yarn. The lightreceived by receivers is converted in a manner known per se intoelectrical signals for which ranges or threshold values can be providedin order, for example, to detect foreign bodies in the yarn.

This device has the disadvantage that, for example, foreign bodies inthe yarn that have the same colour as the emitted light cannot bedetected therewith. However, the same is also true, for example, oftransparent foreign bodies such as pieces of plastics film in the yarn,so that such foreign bodies cannot be detected with this device.

A further device of this type is known from WO 95/29396, in which threedifferent light sources are associated with a receiver for white light.These three light sources are in the form of three light-emittingdiodes, each diode emitting light of a different main wavelength in thevisible range. When viewed in the longitudinal direction of the yarn,the light sources are arranged one behind the other next to the yarn andare so oriented that they illuminate the yarn and a background that islocated behind the yarn and absorbs as much light as possible. Thesignals produced in the receiver by reflection of the light by the yarnare processed in such a manner that ratios are formed from the valuesdetermined for the signals in the individual main wavelengths, whichratios can in turn be measured against criteria.

A particular disadvantage of this device is that it is only suitable forthe evaluation of reflected light with yarn in front of a preferablyblack background. Moreover, the arrangement of three or more diodes atintervals along the yarn requires a large amount of space, which may noteven be available at those locations in textile machines that areintended for such devices. This device has the additional problem thatoperation of the individual light sources must take into account themovement of the yarn and it must therefore be provided that the samepoint on the yarn is always illuminated with light of a differentcolour.

The invention, as characterised in the patent claims, achieves theobject of providing a device of the mentioned type which requires littlespace, is more simple to operate and permits the detection of foreignbodies in the yarn more selectively and with greater sensitivity.

This is achieved according to the invention with a device which providesa single light source for emitting light in at least two wavelengthregions, the wavelength regions being determined by main wavelengths.The main wavelengths determine at least two colours in the region ofwavelengths of visible light. These are preferably the colours red,green or blue. The light source is preferably in the form of alight-emitting diode which is able separately to emit visible light inthree colours in the visible range. The light source and the receiverexhibit principal axes for the emission and reception of light whichtogether define a plane that is transverse to the longitudinal directionof the yarn. The unit for processing electrical signals from thereceiver for reflected light forms a vector in a plane or in a spacefrom the signals in each of the at least two specified wavelengthregions and forms a sum vector from the vectors for the various signals.For the end point of the sum vector in the space there is specified aregion which indicates whether the electrical signal from the receiverprocessed to form the sum vector indicates a foreign body in the yarn.The space in which the vectors are calculated and/or representedpreferably forms a cube with axes along which values for the intensityof three main wavelengths are plotted.

The advantages achieved by the invention are that the single lightsource illuminates the yarn with light having different wavelengths fromvirtually the same point, so that the light beams in all the wavelengthregions strike the yarn within a narrowly limited angle. This lightsource does not require much space either, so that it is possible tobuild a measuring head for yarn that can be installed at a narrowlydelimited location in the spinning machine or spooler. Moreover, thementioned light source is substantially less expensive than a grouphaving one light source for each colour. Because it is also possible toprovide a plurality of receivers which convey the light reflected by theyarn to a unit for processing electrical signals which processes thesesignals in exactly the same manner, it is possible to scan the whole ofthe yarn surface facing the receivers. The use of a plurality ofidentical receivers for white light permits the detection of the coloursof the yarn without spectral errors. The evaluation of the resultingsignals, with the aim of forming a sum vector from the portions of theindividual colours, makes possible the selective detection of foreignbodies of particular colours and colour shades corresponding toparticular materials. However, it is also possible to deliberately leaveforeign bodies in the yarn, by first detecting them or by specifying aregion for the end point of the sum vector so that certain foreignbodies are not detected at all. By the targeted cleaning of the yarn inrespect of particular impurities or foreign bodies, the performance ofthe production machines can be substantially improved.

The invention is explained in greater detail hereinbelow by means of anexample and with reference to the accompanying figures, in which:

FIG. 1 shows a section through a device according to the invention,

FIGS. 2, 3 and 4 each show a diagrammatic representation of part of thedevice in different phases,

FIG. 5 shows a diagrammatic representation of wavelength regions,

FIGS. 6 and 7 each show a diagrammatic representation of the evaluationof the measured signals,

FIG. 8 to 10 each show a representation of a target region for theevaluation, and

FIGS. 11 and 12 each show representations of possible ways of operatingthe light source of the device.

FIG. 1 shows a device according to the invention, such as, for example,a measuring head for measuring yarn properties or for a yarn cleaner,having a measuring gap 1 in which a yarn 2 is moved in its longitudinaldirection, the longitudinal direction here being oriented approximatelyperpendicularly to the drawing plane. A light beam 3 is produced by alight source 4 and is directed towards the yarn 2. Receivers 5 and 6 forlight reflected by the surface of the yarn are provided. The lightsource provided is a light-emitting diode, for example a so-calledRGB-LED, as produced by Nichia (viewable on the Internet atwww.nichia.co.jp) of type NTSM 515. However, it is also conceivable touse other light sources, for example based on a laser. A furtherreceiver 7 can additionally be provided for light shaded by the yarn 2.The receiver(s) 5, 6, 7 is/are each connected by way of a line or a bus8 to a unit 9 for processing electrical signals from the receiver(s).The unit 9 consists of a computer with a memory, that is to say, forexample, of a microprocessor of known type. The light source 4 has fourconnections 10 via which the individual wavelength regions or colourscan be operated individually. In this example, the single light source 4and the receiver 6 have principal axes 11 and 12 for the emission andreception of light which together define a plane that is transverse tothe longitudinal direction of the yarn and here corresponds to thedrawing plane.

FIG. 2 shows, in a simplified representation, the light source 4 withthree light-emitting diodes 13, 14 and 15, and the yarn 2 with a foreignbody 16 embedded therein. Relative to the principal axis 11 of the lightsource 4, the foreign body is located just before the principal axis,starting from a direction of movement indicated by an arrow 17. The yarn2 with the foreign body 16 is here illuminated, for example, by redlight from the diode 13, which emits light in a region 20 as delimitedby lines 18 and 19.

FIG. 3 shows a representation according to FIG. 2 wherein the yarn 2with the foreign body 16 is located approximately at the principal axis11. The yarn 2 with the foreign body 16 is here illuminated, forexample, by green light from the diode 14, which emits light in a region21 as delimited by lines 22 and 23.

FIG. 4 shows a representation according to FIG. 2 wherein the yarn 2with the foreign body 16 is located above the principal axis 11. Theyarn 2 with the foreign body 16 is here illuminated, for example, byblue light from the diode 15, which emits light in a region 24 asdelimited by lines 25 and 26.

FIG. 5 shows a representation of different wavelength regions over anaxis 27, along which values for wavelengths can be plotted. Values forthe intensity of a signal as a function of the wavelength can be plottedalong an axis 28. Three wavelength regions 29, 30 and 31 are recordedhere by way of example by means of curves which indicate the progressionof the intensity of the emitted light in the region of their three mainwavelengths 32, 33 and 34. For the sake of simplicity and for subsequentrepresentations, these wavelength regions can also be represented bysimple rectangles 35, 36 and 37.

FIG. 6 shows a plane 35 defined by axes 36 and 37. Along these axes 36,37, values for the intensity of in each case one colour of the lightfrom the light source 4 reflected by the yarn can be plotted as vectors.A sum vector 38 can be calculated therefrom. In the plane 35, regions39, 40, 41 representing particular properties of the yarn can bespecified. Such properties may be the nature of the base materials ofwhich the yarn consists or the nature of the foreign bodies occurring inthe yarn.

Analogously to FIG. 6, which applies to light from two differentwavelength regions, FIG. 7 shows a space 42, delimited as a cube, forthe representation of vectors which correspond to the intensity of thereceived signals in three different wavelength regions. One corner 43 ofthe space should here serve as the starting point for vectors 44, 45,46, each of which represents a particular wavelength region. 47 denotesa sum vector composed of the three vectors 44, 45 and 46. This space orcube 42 can be divided into different regions. One such region 48 isshown in FIG. 8, one region 49 is shown in FIG. 9 and one region 50 isshown in FIG. 10. These regions 48, 49 and 50 are intended as the targetregion for the end point 51 of the sum vector 47. Depending on whetherthe end point 51 lies in one of these regions 48, 49, 50 or not, aparticular condition for a property of the yarn, such as, for example,the presence of a particular foreign body, is or is not met. The space42, which here is in the form of a cube, is formed by axes 52, 53 and54, along which values for the intensity of three main wavelengths areplotted.

FIG. 11 shows various wavelength regions, as known from FIG. 5, in thiscase plotted over a time axis 55. This gives examples of possiblerepeating sequences for the emission of light by the light source 4.According to a sequence 56, the light source 4 is to emit light of thecolours red, green and blue in succession. A sequence 57 indicates that,over a specified time, red-coloured light is to be emitted withdecreasing intensity and at the same time green-coloured light is to beemitted with increasing intensity. If three colours are used, two orthree sequences with in each case two colours are obtained. When thethree sequences are complete, the first sequence 57 is begun again.

FIG. 12 shows further sequences analogous to FIG. 11. A sequence 58 forthree colours which overlap but together give a specified overallintensity. A sequence 59 again involves three colours which aredesignated R, G and B and which overlap. The intensity of the signals inthe three colours is always constant or maximum.

The mode of operation of the device is additionally to be describedhereinbelow, in so far as it is not already evident from the abovedescriptive parts. In order to detect, for example, a particular foreignbody in or another property of the yarn 2, the light source is operatedby way of the connections 10 in such a manner, for example, that itemits light in only a limited wavelength region. This light is reflectedby the yarn and thrown back to a receiver 5, 6, which receives the lightand converts it into an electrical signal which is passed by way of theline or the bus 8 to the unit 9, which stores the signal or a numericalvalue derived therefrom. Immediately thereafter, the light source 4 isso operated that it emits light in a further wavelength region etc., sothat a further signal or a further value can finally be stored in theunit 9. From the stored values, vectors 44, 45 and, optionally, 46 areformed in the computer of the unit 9, and a sum vector 38 or 47 isfinally formed therefrom. Values that define at least one region 39, 40,41 or 48, 49, 50 in the plane 35 or in the space 42 are stored in theunit 9, so that it is possible, by making a comparison, to determinewhether the end point of the sum vector lies in one of these regions ornot. As a result of such a comparison, a signal can then be emitted bythe unit 9 by way of a line 60, which signal indicates whether, forexample, a desired property is present, for example whether a foreignbody is present in the yarn or not.

If a further receiver 7 for transmitted light is present, that receivermay, for example, emit a further signal to the unit 9 indicating thediameter of the yarn. It is thus also possible, in a known manner, tocompensate for the effect of the diameter of the yarn on the reflectedlight received.

As already shown in FIGS. 11 and 12, there are various possible ways ofoperating the light source 4. If, for example, continuous transitionsbetween two or more wavelength regions are used, as shown in sequences57 and 58, it is then also possible to determine the vectors and the sumvector 38, 47 at different times during the sequence. The sum vector 38,47 accordingly carries out a movement in the plane or in the spaceduring the sequence and it is possible to determine at which times, orin which parts of the wavelength regions, the end point lies within aparticular region 22. Starting from mixed light from two wavelengthregions it is thus also possible to acquire information about propertiesof the yarn which are otherwise not obtainable.

For the separate illumination of the yarn according to a sequence 56,the cycle frequency with which the individual diodes 13, 14, 15 of thelight source 4 are to be operated should be at least so great that thedistance moved by a particular point, such as, for example, the locationat which a foreign body 16 is embedded in the yarn 2, in a particulartime is such that the point still falls within the regions 20, 21 and24. That particular time here lasts three cycles or a multiple thereof.Because the diodes 13 to 15 are arranged extremely close to one anotherin the single light source 4, the time required for illumination withthree wavelength regions is very short and it is accordingly readilypossible to scan such a point three times while it is located in frontof the light source 4.

If the colours red, green and blue are chosen as the wavelength regions,these and further colours can be recognised, in the representationaccording to FIG. 7, in the following arrangement in the space 42:

The intensity of the black colour should be maximum in corner 43. Theintensity of the red colour should be maximum in corner 61. Theintensity of the green colour should be maximum in corner 62. Theintensity of the blue colour should be maximum in corner 63. Theintensity of the colour magenta should be maximum in corner 64. Theintensity of the colour cyan should be maximum in corner 65. Theintensity of the colour yellow should be maximum in corner 66, and theintensity of the white colour should be maximum in corner 67.

It is known per se which formulae can be used to calculate the mentionedvectors. For the sake of completeness, an example is given here. Thefollowing applies to the length of the sum vector 47, as is known fromFIG. 7 and which is here denoted V₄₇:|V₄₇|=√{square root over (|V₄₄|²+|V₄₅|²+|V₄₆|²)}wherein V₄₄, V₄₅ and V₄₆ denote the lengths of the vectors 44, 45 and46. The direction of the sum vector is determined by known rules oftrigonometry. An appropriately adapted calculation can be used for thevectors of FIG. 6.

The position of the sum vector 38, 47 can give an indication, forexample, of whether a foreign body is present, what type it is andwhether it is troublesome and must be removed or not. For example, it ispossible according to FIG. 6 to determine that, for tolerated foreignbodies, the sum vector 38 in FIG. 6 should lie only with its end pointin the region 41 or even in the region 39. In FIGS. 7 to 10 it could beassumed, for example, that the end point 51 of the sum vector 47 shouldlie in a region 68 delimited by an area 69 and close to the corner 67when no foreign body is present and the yarn is white or almost white.If the end point 51 lies in the regions 48, 49 or 50, it is assumed thatthe foreign body is predominantly blue, green or red. However, such aforeign body may nevertheless be tolerable per se. This may be the case,for example, for a red foreign body when the yarn is subsequently to bedyed red.

1. Device for scanning a yarn that is moved in its longitudinaldirection in a measuring gap with a light beam from a light source,comprising a receiver for light reflected at the yarn, a unit forprocessing electrical signals from the receiver, and a single lightsource for emitting light in at least two wavelength regions, thewavelength regions being determined by two main wavelengths, said unitfor processing electrical signals from the receiver including a computerwhich forms a vector from the values for each of the at least twospecified wavelength regions and forms a sum vector from the vectors. 2.Device according to claim 1, wherein the main wavelengths determine twocolours in the region of wavelengths of visible light.
 3. Deviceaccording to claim 2, wherein the main wavelengths relate to the coloursred, green and blue.
 4. Device according to claim 1, wherein the singlelight source is in the form of a light-emitting diode which is ableseparately to emit visible light in three colours in the visible range.5. Device according to claim 1, wherein the single light source and areceiver have principal axes for the emission and reception of lightwhich together span a plane that is transverse to the longitudinaldirection of the yarn.
 6. Device according to claim 1, wherein for theend point of the sum vector in a space a region is delimited whichindicates whether the electrical signal from the receiver processed toform the sum vector indicates a foreign body in the yarn.
 7. Deviceaccording to claim 6, wherein the space forms a cube which is formed byaxes along which values for the intensity of three main wavelengths areplotted.